Musnad Ahmed: Hadith 2881

Abdullah bin 'Abbas passed by Abdullah bin al- Harith bin Abi Rabee'ah when he was praying with his hair in braids, tied at the back. He stood over him and started undoing the braids, and 'Abdullah bin al-Harith let him carry on until he had finished undoing it and then sat down. When Ibn al-Harith finished praying, he came to him and said: Why did you do what you did to my head just now? He said: I heard the Messenger of Allah (ﷺ) say: "The likeness of the one who prays with his hair tied up at the back is like one who prays with his hands tied behind his back.”